Bright tin-nickel alloy plating electrolyte

ABSTRACT

A bright tin-nickel alloy plating electrolyte consists essentially of an aqueous main plating liquid containing a stannous salt, a nickel salt and an alkali-metal pyrophosphate, with a brightener additive in such main plating liquid which is a compound having a plurality of amino groups, for example, ethylenediamine, 1,2-propanediamine, 1,3-propanediamine, 1,4butanediamine, pentamethylenediamine, hexamethylenediamine, hydrazine, guanidine, urea or thiourea, and with a further addition of ammonia or an ammonium salt. The electrolyte may further have added thereto a compound having at least one -SX group in this electrolyte (in which X represents hydrogen, sodium or potassium), a peptone and/or protein, or a neutral amino acid which is free of sulphur or a salt thereof.

United States Patent [191 Fueki et al.

[ June 3, 1975 BRIGHT TIN-NICKEL ALLOY PLATING ELECTROLYTE [73] Assignee: Sony Corporation, Tokyo, Japan [22] Filed: Apr. 12, 1974 [2l] Appl. No.: 460,527

[30] Foreign Application Priority Data Apr. 19, I973 Japan .f. 48-43776 [52] US. Cl. 204/43 S [51] Int. Cl. C23b 5/38; C23b 5/46 [58] Field Of Search 204/43 S. 43 T References Cited UNITED STATES PATENTS 3,772,168 11/1973 Dillenberg 204/43 S FOREIGN PATENTS OR APPLICATIONS 248,415 12/1969 U.S.S.R. 204/43 S Primary ExaminerG. L. Kaplan Attorney, Agent, or Firm-Lewis H. Eslinger; Alvin Sinderbrand [57]' ABSTRACT A bright tin-nickel alloy plating electrolyte consists essentially of an aqueous main plating liquid containing a stannous salt, a nickel salt and an alkali-metal pyrophosphate, with a brightener additive in such main plating liquid which is a compound having a plurality of amino groups, for example, ethylenediamine, 1,2- propanediamine, 1,3-propanediamine, l ,4- butanediamine, pentamethylenediamine, hexamethylenediamine, hydrazine, guanidine, urea or thiourea, and with a further addition of ammonia or an ammonium salt. The electrolyte may further have added thereto a compound having at least one SX group in this electrolyte (in which X represents hydrogen, sodium or potassium), a peptone and/or protein. or a neutral amino acid which is free of sulphur or a salt thereof.

14 Claims, No Drawings BRIGHT TIN-NICKEL ALLOY PLATING ELECTROLYTE BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to a bright tin-nickel plating electrolyte, and more particularly to an aqueous pyrophosphate electroplating bath for obtaining a bright tin-nickel alloy plating.

2. Description of the Prior Art An acid fluoride bath-is generally used for achieving a tin-nickel alloy plating, but an electroplated layer formed from such bath is very brittle and is apt to crack when a stress is exerted thereon, for example, due to flexing of the plating substrate. Further, a tin-nickel alloy acid bath including a fluoride is disadvantageous in that it requires difficult and expensive treatment of exhaust fumes and of the aqueous bath prior to discharge thereof into the atomsphere and adjacent sewer or waterway, respectively, for avoiding pollution of the environment.

It is also known to provide a tin-nickel alloy plating electrolyte which has, as its main component, an aqueous plating liquid containing a stannous salt, a nickel salt and an alkali-metal pyrophosphate. with the addition thereto, as a brightening agent, of ammonium citrate and/or gelatine, and ot-amino acid such as glycine, or an a-amino acid and a mercaptan derivative. However, such aqueous pyrophosphate bath, even when containing one or more of the mentioned brightening agents, is incapable of producing a tin-nickel alloy plating of high brightness.

SUMMARY OF THE INVENTION Accordingly, it is an object of this invention to provide a bright tin-nickel alloy plating electrolyte which is capable of producing a plating layer of improved toughness, flexibility and brightness.

Another object is to provide a bright tin-nickel alloy plating electrolyte, as aforesaid, which is free of any fluorides so as to minimize the ecological problems resulting from its use.

A further object is to provide a bright tin-nickel alloy plating electrolyte having, as its main component, an aqueous plating liquid containing stannous and liquid salts and an alkali-metal pyrophosphate, with a bright- "ener additive which results in a plating layer of exvention, with or without the addition may further advantageously contain a compound having SX groups in such electrolyte, in which X represents hydrogen, so-

dium or potassium, peptone and/or a protein, or a neutral amino acid without sulphur or a salt of such neutral amino acid.

In the bright tin-nickel alloy plating electrolyte according to the invention, the stannous salt maybe present in the main plating liquid in an amount between 2 and calculated calucated as stannous ion; the nickel salt may be present in the main plating liquid in an amount between 5 and 30 g/l., calculated as nickel ion, and the alkali-metal pyrophosphate may be present in the main plating liquid in an amount between 150 and 600 g/l. The alkali-metal pyrophosphate of the main plating liquid may be, for example, potassium pyrophosphate or sodium pyrophosphate, while the stannous and nickel salts of such main plating liquid may be respectively stannous pyrophosphate. stannous chloride, stannous sulfate or the like, and nickel pyrophosphate, nickel chloride, nickel sulfate or the like.

The brightener additive which is essentially added to the main plating liquid and which, in accordance with this invention, contains a plurality of amino groups may be advantageously selected from the group consisting of ethylenediamine, 1,2-propanediamine, 1,3- propanediamine, 1,4-butanediamine, pentamethylenediamine, hexamethylenediamine, hydrazine, guanidine, urea and thiourea. The amount of such brightener additive introduced into the main plating liquid is preferably between0.l and g/l. of the main plating liquid.

The ammonia added to the plating electrolyte may be in the form of 28 percent aqueous ammonia solution in the amount between 5 and 100 g/l. of the main plating liquid. When ammonium salt is added, such addition may be ammonium chloride, ammonium sulfate, ammonium nitrate, ammonium citrate, ammonium tartrate, ammonium acetate or the like, and is present in an amount between 1.0 and g/l. of the main plating liquid.

The compound having SX groups in the electrolyte and which may be optionally added to the bright tinnickel alloy plating electrolyte according to this invention may be advantageously selected from among dithioammelide, 4-amino-3,5-dimercapto-l ,2,4-triazole, ethylene thiuram monosulfide, 2,5-dimercapto-1,3,4- thiadiazole, thiocarbohydrazide, hydrazodithiodicarbonamide, ethylenebis-dithiocarbamic acid sodium salt and the like, and is added in an amount between 0.01 and 5 g/l. of the main plating liquid.

When peptone and/or protein is added to the electrolyte, the amount thereof is between 0.1 and 10 g/l. of the main plating liquid. The protein thus added may be, for example, glue, gelatine or gluten. The peptone and- /or protein is prferably dissolved in water, in an aqueous solution of potassium pyrophosphate or in an alcohol, such as, methanol or ethanol, before being added to the main plating liquid of the electrolyte.

When a neutral amino acid without sulphur is added to the electrolyte according to this invention, such additive may be advantageously selected from glycine. alanine, serine. aminobutyric acid, leucine. isoleucine. proline. hydroxyproline, phenylpalanine, thyroxine. tryptophan and the like, and is added in an amount greater than 0.01 mol/l. of the main plating liquid.

The pH of the plating electrolyte is adjusted to within the range of 8 to 12 with aqueous ammonia solution. caustic potash, pyrophosphoric acid and the like.

The invention is further described with reference to the following specific examples thereof:

EXAMPLE 1 An aqueous main plating liquid is provided containing 200 g/l. of potassium pyrophosphate. 30 g/l. of stannous pyrophosphate and 50 g/l. of nickel pyrophosphate. Such main plating liquid has added thereto 15 g/l. of ethylenediamine, which is added as an 85 per- EXAMPLES 2,3 and 4 The procedures described above in Example l are repeated, but with the further addition to the main plating liquid of ammonium chloride (Examples'Z and 4) or aqueous ammonia (Example 3) and with the substitution of nickel chloride for the nickel pyrophosphate (Examples 3 and 4), and the results thereof are as shown on Table 1 below.

. '4 The procedure of Example 1,2,3 and 4 are repeated. but using, in turn, hydrazine, 1.2-propahediamine, 1,3- propanediamine, 1,4-butanediamine; guanidine, urea, thiourea, pentamethylenediamine and hexamethylenediamine. in place of the ethylene diamine, and, in each case, a bright tin-nickle alloy plating similar in appearance to the platings obtained in Examples 1,2,3 and 4 on Table 1 is obtained.

EXAMPLES 5,678 and 9 The procedures described in Example 1 are repeated, but with nickel chloride replacing the nickel pyrophosphate (Examples 7,8 and'9), and with the further addition ofa compound having an SX group. to wit, 2,5-

5 dimercapto-l,3,4-thiadiazole (Examples 5,6 and 9),

dithioammelide (Examples 7 and 9) and hydrazodithiodicarbonamide (Example 8), and the proportions and results of such additives areas shown on Table 2 below.

- TABLE 1 Examples 1 2 3 4 Potassium pyrophosphate g/l. 200 200 200 200 Stannous pyrophosphate g/l. 30 30 30 30 Nickel pyrophosphate g/l. 50 50 Nickel chloride g/l. 40 40 Ethylenediamine of 85% g/l. l5 15 25 Ammonium chloride g/l. 2O 50 Aqueous ammonia of 28% cell 20 p 9.5 9.5 9.5 9 5 Temperature C 30 30 3O Agitation Yes Yes No No Current density A/dm 0.5 0.5 0.5 0,5 Anode carbon carbon carbon carbonv Amount of tin contained in deposited alloy '/r 67.2 62.1 66.3 67.1 Appearance Bright Bright Bright Bright stainless stainless Stainless stainless color color color color similar to white TABLE 2 Examples 5 6 7 8 9 Potassium pyrophosphate 200 200 1 200 200 200 g/l. Stannous ro hos hate W p p g/l. 30 30 30 30 30 Nickel pyrophosphate g/l. 50 50 Nickel chloride g/l. 40 I 40 40 Ethylenediamine of 857:

v g/l. 0.8 0.8 0.8 0.8 1 2,5-dimercapto- 1,3,4-

thiodiazole g/l. 0.5 0.5 0.5 Dithioammelide g/l. 1 0.5 Hydrazodithiocarbonamide g/l. 1 pH 9 9.5 9.5 r 9 5 Temperature "C 35 35 35 3S Agitation Yes Yes Yes. Yes Yes Current density A/dm 0.5 0.2 0.5 0.5 0.5 Amount of tin contained in deposited alloy 7! 72.1 71.5 73.1 70.1 I 70.3 Appearance Bright Bri ht Bright Bright Bright stainless stain ess stainless stainless stainless color color color color color with with with with 1 with black black black black black EXAMPLES 10.11.12.13 and 14 The procedures of Example 1 are repeated. but with the further addition of a compound having one or more -SX groups in this electrolyte to wit. 2.5-dimercapto- 5 1.3,4-thiadiazole (Examples l0,l2,13 and 14) an dithioammelide (Examples 1 l. 13 and 14) and of either ammonium chloride (Examples 10.1 1 and 14) or aqueous ammonia (Examples 12 and 13), and the pro d/or por-

EXAMPLES l8 and 19 The procedures of Example 1 are repeated, but with the further addition of a neutral amino acid free of sulphur or a salt thereof, to wit. sodium glycine (Example 18) or alanine (Example 19). and also of aqueous ammonia (Example 19), and the proportions and results tions and results of such further additives are as shown of such further additions are as shown on Table 5 beon Table 3 below.

TABLE 3 Examples 10 l l l2 l3 l4 Potassium Pyrophosphate g/l. 200 200 200 200 200 Stannous pyrophosphate g/l. 3O 30 30 30 Nickel pyrophosphate g/l. 50 50 50 Nickel chloride g/l. 40 40 Etlylenediamine of 85 r g/l. 0.8 0.8 0.8 0.8 0.8 2.5-dimercapto- Y 1,3,4-thiadiazole g/l. 0.5 0.5 0.5 l Dithioammelide g/l. 0.5 0.5 0.5 Ammonium chloride g/l. 50 5O Aqueous ammonia of 28% cc/l. 3O 30 P 9.5 9.5 9.5 9.5 9.5 Temperature C 35 35 35 35 35 Agitation Yes Yes Yes Yes Yes Current density A/dm 0.5 0.5 0.5 0.5 0.5 Amount of tin contained in deposited alloy 71 67.8 64.2 64.8 63.5 65.4

Bright Bright Bright Bright Bright Appearance stainless stainstainstainstaincolor less less less less color color color color TABLE 5 Examples Reference Potassiumpyrophosphate g/l. 200 200 200 Stannous pyrophosphate g/l. 3O 3O 30 Nickel pyrophosphate g/l. 5O 50 50 Ethylenediamine of g/l. 0.8 0.8 Sodium glycine g/l. 7 7 Alanine g/l. 8 Aqueous ammonia of 28% cell. 30

EXAMPLES 15.16 and 17 The P es of Example 1 are repeated, but with '45 the further addition of peptone (Examples 15 and or demed P ein in the form of glue (Example and also of ammonium chloride (Example 17) and the proportions and results of such additives are as shown black TABLE Continued Examples Reference l8 I9 I pH 9.5 9.5 9.5 Temperature C 35 35 35 Agitation Yes Yes Yes Current density A/dm 0.5 0.5 0.5 Anode carbon carbon carbon Amount of tin contained in deposited alloy 67.4 68.2 84.2 Appearance Bright Bright Grey stainless stainless with no color color brightness REFERENCE 1 In order to demonstrate the essential character of the additive compound having a plurality of amino groups, the procedure of Example 18 was repeated, but with the ethylenediamine being omitted from the plating electrolyte and, as shown on Table 5 above, the resulting plating layer was grey in color and devoid of brightness.

Thus, it will be apparent that, by the addition to the main plating liquid, containing stannous salt, nickel salt and an alkali-metal pyrophosphate, of a compound having a plurality of amino groups, the present invention produces a bright tin-nickel alloy plating layer with a brightness that cannot be obtained with prior plating electrolytes.

Further, it will be apparent that the brightness of the tin-nickel alloy plating layer is further enhanced by also adding to the electrolyte a compound having one or more -SX groups in this electrolyte (in which X represents hydrogen, sodium or potassium), peptone and/or protein, or a neutral amino acid free of sulphur.

Finally, the further addition of ammonia or ammonium salt to the plating electrolyte according to this invention is shown to provide the bright plating layer with white color.

Although specific examples of the invention have been described in detail herein, it is to be understood that the invention is not limited to those precise examples which are intended to be illustrative, and that a person skilled in the art may effect various changes and variations or modifications in the given examples without departing from the scope or spirit of the invention as defined in the appended claims.

What is claimed is:

l. A bright tin-nickel alloy plating electrolyte having a pH in the range from 8 to 12 and consisting essentially of an aqueous main plating liquid containing:

a. a stannous salt selected from the group consisting of stannous pyrophosphate, stannous chloride and stannous sulfate, and which is present in said main plating liquid in an amount between 2 and 20 g/l. calculated as stannous ion;

b. a nickel salt selected from the group consisting of nickel pyrophosphate, nickel chloride and nickel sulfate, and which is present in said main plating liquid in an amount between 5 and 30 g/l. calculated as nickel ion;

c. an alkali-metal pyrophosphate selected from the group consisting of potassium pyrophosphate and sodium pyrophosphate, and which is present in said main plating liquid in an amount between 150 and 600 g/l;

d. at least one brightener additive in said plating liquid in an amount between 0.1 and 100 g/l. of said main plating liquid and being selected from the group consisting of ethylenediamine, 1,2- 2 propanediamine, 1,3-pr0panediamine, 1,4- butanediamine, pentamethylenediamine, hexamethylenediamine, hydrazine, quanidine, urea and thiourea; and e. a further additive selected from the group consisting of ammonia and ammonium salts, and in which said further additive is present in said main plating liquid in the amount between 5 and 100 g/l. in the case of ammonia calculated as a 28 percent aqueous ammonia solution, and between 1 and 150 g/l. 30 in the case of ammonium salts.

2. A bright tin-nickel alloy plating electrolyte according to claim 1, in which said main plating liquid further contains a compound having at least one --SX group in said electrolyte, in which X represents hydrogen, sodium or potassium, and being present in said main plating liquid in an amount between 0.01 and 5 g/l.

3. A bright tin-nickel alloy plating electrolyte according'to claim 2, in which said compound having at least one -SX group in said electrolyte is selected from the group consisting of dithioammelide, 4-amino-3,5-dimercapto-l,2,4-triazole, ethylene thiuram monosulfide, 2,5-dimercapto-l,3,4-thiadiazole, thiocarbohydrazide, hydrazo-dithiodicarbonamide, and ethylene-bis-dithiocarbamic acid sodium salt.

4. A bright tin-nickel alloy plating electrolyte according to claim 1, in which said main plating liquid further contains at least one substance selected from the group consisting of peptones and derived proteins and which is present in said main plating liquid in an amount between 01 and 10 g/l.

5. A bright tin-nickel alloy plating electrolyte according to claim 4, in which said at least one substance is a derived protein selected from the group consisting of glue, gelatine and gluten.

6. A bright tin-nickel alloy plating electrolyte according to claim 1, in which said main plating liquid further contains a substance selected from the group consisting of neutral amino acids which are free of sulphur, and salts thereof, and said substance is present in said main plating liquid in an amount greater than 0.0] mol/l.

7. A bright tin-nickel alloy plating electrolyte according to claim 6, in which said substance is selected from the group consisting of glycine, alanine, serine, aminobutyric acid, leucine, isoleucine, proline, hydroxyproline, phenyl-alanine, thyroxine and tryptophan, and salts thereof.

8. A bright tin-nickel alloy plating electrolyte according to claim 1, in which said ammonium salt is selected from the group consisting of ammonium chloride. ammonium sulfate, ammonium nitrate, ammonium citrate, ammonium tartrate and ammonium acetate.

9. A bright tin-nickel alloy plating electrolyte having a pH in the range from 8 to 12 and consisting essentially of an aqueous main plating liquid containing:

a. a stannous salt selected from the group consisting of stannous pyrophosphate, stannous chloride and stannous sulfate, and which is present in said main plating liquid in an amount between 2 and 20 g/l. calculated as stannous ion;

b. a nickel salt selected from the group consisting of nickel pyrophosphate, nickel chloride and nickel sulfate, and which is present in said main plating liquid in an amount between 5 and 30 g/l. calculated as nickel ion;

c. an alkali-metal pyrophosphate selected from the group consisting of potassium pyrophosphate and sodium pyrophosphate, and which is present in said main plating liquid in an amount between 150 and 600 g/l.;

d. at least one brightener additive in said plating liquid in an amount between 0.1 and 100 g/l. of said main plating liquid and being selected from the group consisting of ethylene-diamine, 1,2- propanediamine, l,3-propanediamine, 1,4- butanediamine, pentamethylenediamine, hexamethylenediamine, hydrazine, guanidine, urea and thiourea; and

e. a compound having at least one SX group in said electrolyte, in which X represents hydrogen, sodium or potassium, and which is present in said main plating liquid in an amount between 0.1 and 5 g/l.

10. A bright tin-nickel alloy plating electrolyte according to claim 9, in which said compound having at least one SX group in said electrolyte is selected from the group consisting of dithioammelide, 4-amino-3,5-dimercapto-l,2,4-triazole, ethylene thiuram monosulfide, 2,5-dimercapto-l,3,4-thiadiazole, thiocarbohydrazide, hydrazodithiodicarbonamide, and ethylene-bis-dithiocarbamic acid sodium salt.

11. A bright tin-nickel alloy plating electrolyte having a pH in the range from 8 to 12 and consisting essentially of an aqueous main plating liquid containing:

a. a stannous salt selected from the group consisting of stannous pyrophosphate, stannous chloride and stannous sulfate, and which is present in said main plating liquid in an amount between 2 and g/l. calculated as stannous ion;

b. a nickel salt selected from the group consisting of nickel pyrophosphate, nickel chloride and nickel sulfate, and which is present in said main plating liquid in an amount between 5 and g/l. calculated as nickel ion;

0. an alkali-metal pyrophosphate selected from the group consisting of potassium pyrophosphate and sodium pyrophosphate, and which is present in said main plating liquid in an amount between 150 and 600 g/L;

d. at least one brightener additive in said plating liquid in an amount betwen Oil and g/l. of said main plating liquid and being selected from the group consisting of ethylene-diamine, 1,2- propanediamine, 1,3-propanediamine, 1,4- butanediamine, pentamet hylenediamine. hexamethylenediamine, hydrazine, quanidine, urea and thiourea; and

e. at least one substance selected from the group consisting of peptones and derived proteins and which is present in said main plating liquid in an amount between 0.1 and 10 g/l.

12. A bright tin-nickel alloy plating electrolyte according to claim 11, in which said at least one substance is a derived protein selected from the group consisting of glue, gelatine and gluten.

13. A bright tin-nickel alloy plating electrolyte having a pH in the range from 8 to 12 and consisting essentially of an aqueous main plating liquid containing:

a. a stannous salt selected from the group consisting of stannous pyrophosphate, stannous chloride and stannous sulfate, and which is present in said main plating liquid in an amount between 2 and 20 g/l. calculated as stannous ion;

b. a nickel salt selected from the group consisting of nickel pyrophosphate, nickel chloride and nickel sulfate, and which is present in said main plating liquid in an amount between 5 and 30 g/l. calculated as nickel ion;

c. an alkali-metal pyrophosphate selected from the group consisting of potassium pyrophosphate and sodium pyrophosphate, and which is present in said main plating liquid in an amount between and 600 g/L;

d. at least one brightener additive in said plating liquid in an amount between 0.1 and 100 g/l. of said main plating liquid and being selected from the group consisting of ethylene-diamine, 1,2- propanediamine, l,3-propanediamine, l ,4- butanediamine, pentamethylenediamine, hexamethylenediamine, hydrazine, quanidine, urea and thiourea; and e. a substance selected from the group consisting of neutral amino acids which are free of sulphur, and salts thereof, and which is present in said main plating liquid in an amount greater than 0.01 mol/l. 14. A bright tin-nickel alloy plating electrolyte according to claim 13, in which said substance is selected from the group consisting of glycine, alanine. scrine. aminobutyric acid, leucine, isoleucine, proline. hydroxyproline, phenylalanine, thyroxine and tryptophan, and

salts thereof. 

1. A BRIGHT TIN-NICKEL ALLOY PLATING ELECTROYLTE HAVING A PH IN THE RANNGE FROM 8 TO 12 AND CONSISTING ESSENTIALLY OF AN AQUEOUS MAIN PLATING LIQUID CONTAINING: A. A STANNOUS SALT SELECTED FROM THE GROUP CONSISTING OF STANNOUS PYROPHOSPHATE, STANNOUS CHLORIDE AND STANNOUS SULFATE, AND WHICH IS PRESENT IN SAID MAIN PLATING LIQUID IN AN AMOUNT BETWEEN 2 AND 20 G/L. CALCULATED AS STANNOUS ION: B. A NICKEL SALT SELECTED FROM THE GROUP CONSISTING OF NICKEL PYROPHOSPHATE, NICKEL CHLORIDE AND NICKEL SULFATE,AND WHICH IS PRESENT IN SAID MAIN PLATING LIQUID IN AN AMOUNT BETWEEN 5 AND 30 G/L. CALCULATED AS NICKEL ION; C. AN ALKALI-METAL PYROPHOSPHATE SELECTED FROM THE GROUP CONSISTING OF POTASSIUM PYROPHOSPHATE AND SODIUM PYROPHOSPHATE, AND WHICH IS PRESENT IN SAID MAIN PLATING LIQUID IN AN AMOUNT BETWEEN 150 AND 600 G/L; D. AT LEAST ON BRIGHTERNER ADDITIVE IN SAID PLATING LIQUID IN AN AMOUNT BETWEEN 0.1 AND 100 G/L. OF SAID MAIN PLATING LIQUID AND BEING SELECTED FROM THE GROUP CONSISTING OF ETHYLENEDIAMINE, 1,2-PROPANEDIAMINE, 1,3PROPANEDIAMINE, 1,4-BUTANEDIAMINE, HYDRAZINE, QUANIDINE, AMINE, HEXXAMETHYLENEDIAMINE, HYDRAZINE, QUANDINE, UREA AND THIOUREA; AND E. A FURTHER ADDITIVE SELECTED FROM THE GROUP CONSISTING OF AMMONIA AND AMMONIUM SALTS, AND IN WHICH SAID FURTHER ADDITIVE IS PRESENT IN SAID MAIN PLATING LIQUID IN THE AMOUNT BETWEEN 5 AND 100 G/L. IN THE CASE OF AMMONIA CALCULATED AS A 28 PERCENT AQUEOUS AMMONIA SOLUTION, AND BETWEEN 1 AND 150 G/L. IN THE CASE OF AMMONIUM SALTS.
 1. A bright tin-nickel alloy plating electrolyte having a pH in the range from 8 to 12 and consisting essentially of an aqueous main plating liquid containing: a. a stannous salt selected from the group consisting of stannous pyrophosphate, stannous chloride and stannous sulfate, and which is present in said main plating liquid in an amount between 2 and 20 g/l. calculated as stannous ion; b. a nickel salt selected from the group consisting of nickel pyrophosphate, nickel chloride and nickel sulfate, and which is present in said main plating liquid in an amount between 5 and 30 g/l. calculated as nickel ion; c. an alkali-metal pyrophosphate selected from the group consisting of potassium pyrophosphate and sodium pyrophosphate, and which is present in said main plating liquid in an amount between 150 and 600 g/l; d. at least one brightener additive in said plating liquid in an amount between 0.1 and 100 g/l. of said main plating liquid and being selected from the group consisting of ethylenediamine, 1, 2-propanediamine, 1,3-propanediamine, 1,4-butanediamine, pentamethylenediamine, hexamethylenediamine, hydrazine, quanidine, urea and thiourea; and e. a further additive selected from the group consisting of ammonia and ammonium salts, and in which said further additive is present in said main plating liquid in the amount between 5 and 100 g/l. in the case of ammonia calculated as a 28 percent aqueous ammonia solution, and between 1 and 150 g/l. in the case of ammonium salts.
 2. A bright tin-nickel alloy plating electrolyte according to claim 1, in which said main plating liquid further contains a compound having at least one -SX group in said electrolyte, in which X represents hydrogen, sodium or potassium, and being present in said main plating liquid in an amount betWeen 0.01 and 5 g/l.
 3. A bright tin-nickel alloy plating electrolyte according to claim 2, in which said compound having at least one -SX group in said electrolyte is selected from the group consisting of dithioammelide, 4-amino-3,5-dimercapto-1,2,4-triazole, ethylene thiuram monosulfide, 2,5-dimercapto-1,3,4-thiadiazole, thiocarbohydrazide, hydrazo-dithiodicarbonamide, and ethylene-bis-dithiocarbamic acid sodium salt.
 4. A bright tin-nickel alloy plating electrolyte according to claim 1, in which said main plating liquid further contains at least one substance selected from the group consisting of peptones and derived proteins and which is present in said main plating liquid in an amount between 0.1 and 10 g/l.
 5. A bright tin-nickel alloy plating electrolyte according to claim 4, in which said at least one substance is a derived protein selected from the group consisting of glue, gelatine and gluten.
 6. A bright tin-nickel alloy plating electrolyte according to claim 1, in which said main plating liquid further contains a substance selected from the group consisting of neutral amino acids which are free of sulphur, and salts thereof, and said substance is present in said main plating liquid in an amount greater than 0.01 mol/l.
 7. A bright tin-nickel alloy plating electrolyte according to claim 6, in which said substance is selected from the group consisting of glycine, alanine, serine, aminobutyric acid, leucine, isoleucine, proline, hydroxyproline, phenyl-alanine, thyroxine and tryptophan, and salts thereof.
 8. A bright tin-nickel alloy plating electrolyte according to claim 1, in which said ammonium salt is selected from the group consisting of ammonium chloride, ammonium sulfate, ammonium nitrate, ammonium citrate, ammonium tartrate and ammonium acetate.
 9. A bright tin-nickel alloy plating electrolyte having a pH in the range from 8 to 12 and consisting essentially of an aqueous main plating liquid containing: a. a stannous salt selected from the group consisting of stannous pyrophosphate, stannous chloride and stannous sulfate, and which is present in said main plating liquid in an amount between 2 and 20 g/l. calculated as stannous ion; b. a nickel salt selected from the group consisting of nickel pyrophosphate, nickel chloride and nickel sulfate, and which is present in said main plating liquid in an amount between 5 and 30 g/l. calculated as nickel ion; c. an alkali-metal pyrophosphate selected from the group consisting of potassium pyrophosphate and sodium pyrophosphate, and which is present in said main plating liquid in an amount between 150 and 600 g/l.; d. at least one brightener additive in said plating liquid in an amount between 0.1 and 100 g/l. of said main plating liquid and being selected from the group consisting of ethylene-diamine, 1,2-propanediamine, 1,3-propanediamine, 1,4-butanediamine, pentamethylenediamine, hexamethylenediamine, hydrazine, guanidine, urea and thiourea; and e. a compound having at least one -SX group in said electrolyte, in which X represents hydrogen, sodium or potassium, and which is present in said main plating liquid in an amount between 0.1 and 5 g/l.
 10. A bright tin-nickel alloy plating electrolyte according to claim 9, in which said compound having at least one -SX group in said electrolyte is selected from the group consisting of dithioammelide, 4-amino-3,5-dimercapto-1,2,4-triazole, ethylene thiuram monosulfide, 2,5-dimercapto-1,3,4-thiadiazole, thiocarbohydrazide, hydrazodithiodicarbonamide, and ethylene-bis-dithiocarbamic acid sodium salt.
 11. A bright tin-nickel alloy plating electrolyte having a pH in the range from 8 to 12 and consisting essentially of an aqueous main plating liquid containing: a. a stannous salt selected from the group consiSting of stannous pyrophosphate, stannous chloride and stannous sulfate, and which is present in said main plating liquid in an amount between 2 and 20 g/l. calculated as stannous ion; b. a nickel salt selected from the group consisting of nickel pyrophosphate, nickel chloride and nickel sulfate, and which is present in said main plating liquid in an amount between 5 and 30 g/l. calculated as nickel ion; c. an alkali-metal pyrophosphate selected from the group consisting of potassium pyrophosphate and sodium pyrophosphate, and which is present in said main plating liquid in an amount between 150 and 600 g/l.; d. at least one brightener additive in said plating liquid in an amount betwen 0.1 and 100 g/l. of said main plating liquid and being selected from the group consisting of ethylene-diamine, 1,2-propanediamine, 1,3-propanediamine, 1,4-butanediamine, pentamethylenediamine, hexamethylenediamine, hydrazine, quanidine, urea and thiourea; and e. at least one substance selected from the group consisting of peptones and derived proteins and which is present in said main plating liquid in an amount between 0.1 and 10 g/l.
 12. A bright tin-nickel alloy plating electrolyte according to claim 11, in which said at least one substance is a derived protein selected from the group consisting of glue, gelatine and gluten.
 13. A bright tin-nickel alloy plating electrolyte having a pH in the range from 8 to 12 and consisting essentially of an aqueous main plating liquid containing: a. a stannous salt selected from the group consisting of stannous pyrophosphate, stannous chloride and stannous sulfate, and which is present in said main plating liquid in an amount between 2 and 20 g/l. calculated as stannous ion; b. a nickel salt selected from the group consisting of nickel pyrophosphate, nickel chloride and nickel sulfate, and which is present in said main plating liquid in an amount between 5 and 30 g/l. calculated as nickel ion; c. an alkali-metal pyrophosphate selected from the group consisting of potassium pyrophosphate and sodium pyrophosphate, and which is present in said main plating liquid in an amount between 150 and 600 g/l.; d. at least one brightener additive in said plating liquid in an amount between 0.1 and 100 g/l. of said main plating liquid and being selected from the group consisting of ethylene-diamine, 1,2-propanediamine, 1,3-propanediamine, 1,4-butanediamine, pentamethylenediamine, hexamethylenediamine, hydrazine, quanidine, urea and thiourea; and e. a substance selected from the group consisting of neutral amino acids which are free of sulphur, and salts thereof, and which is present in said main plating liquid in an amount greater than 0.01 mol/l. 